For those who demand a spine on tiny booklets, there are some binderies who can give you a square-backed saddle-wire book. The example shown, my cheque book register, is slightly odd. Why on earth would the bank want me to have a square-back register to list my payments in? I guess the printer just has the equipment and uses it willy nilly. The only difference from a regular saddle-wired book is the double crease applied to the cover, to mimic a spine, before the booklet is assembled and goes into the binder. The real point of having a spine on such a booklet would be so that you can print the title on the spine, even though the wires will block out some of it. Who can read a title small enough to fit on such a spine is a question best addressed to the marketing folks who tend to demand this sort of thing.

For other styles of binding search “binding styles”.